Dominantly acting enhancer genes which confer increases susceptibility to induced mammary cancer have been characterized in Wistar-Furth (W/Fu) rats, while the presence of a dominantly acting suppressor gene has been confirmed in Copenhagen (Cop) rats. Using chimertic rats the W/Fu enchancer genes were shown to act within the mammary parenchyma. Both gene types were shown not to modify carcinogen metabolism or DNA adduction in mammary cells. The long-term goal of this continuing project is to identify and mechanistically characterize specific genetically controlled factors which modulate susceptibility to mammary cancer. The role of enhancer and suppressor genes in the process of mammary carcinogenesis is the focus of this current proposal. Specific aims include the continued investigation of the pattern of inheritance of these genes and their ability to interact in F1 hybrid rats. Hypotheses which account for tumor development in rats that are heterozygous but not homozygous for the suppressor gene will be explored. Chimeric rats will be constructed and tested to determine if the suppressor gene product is being produced within the mammary parenchyma. The ability of normal mammary cells containing either enchancer or suppressor genes to modify later stages of carcinogenesis in chemically initiated mammary cells lacking both gene types will be explored using chimeric animals with mixed mammary cell grafts. Effects of these genes on possible initiation events will continue to be examined by quantitating specific DMBA-DNA adduct formation, removal, and persistence in mammary epithelial cells. DNA adducts will be examined both by HPLC and 32P-postlabeling methods. Suppressor genes are often equated with anti-onco-genes. This relationship will be explored by attempting to transform mammary cells with and without suppressor genes, using electroporation to transfect with plasmids containing promoter- controlled oncogenes. Finally, candidate gene products of the enhancer and suppressor genes will be identified using computer analyzed 2-D gel electrophoresis. These proteins will be isolated on preparative gels and microsequenced for future investigations in which the genes will be cloned and reintroduced in vivo for phenotypic characterization. This continuing project should provide new information that will help delineate the etiology of breast cancer, a major lethal cancer of women. In addition, the identification of enhancer or suppressor gene products may lead to the development of new strategies in the prevention and treatment of this disease.